In order to reduce the impact on the environment and to protect groundwater and where it is intended to reuse wastewater and to save money, it is necessary to purify contaminated water. This type of treatment/purification can be achieved by means of mechanical and biological treatment of the wastewater. For this purpose, centralized sewage treatment plants are known which at a central location effect the purification of wastewater from a large number of households or consumers. Local decentralized plants are also known which permit provision of a wastewater treatment plant for individual or a plurality of interconnected households. The small construction size thereof permits only a small flow rate volume of wastewater per unit of time, however by reason of their size and because it makes the use of sewers obsolete and due to their relatively uncomplicated structure they can be provided set-up cost-effectively. The present invention relates in particular to such wastewater treatment plants which are to be set up locally. Those wastewater treatment plants can be formed as so-called planted or unplanted soil filters which, for biological purification, utilise layers of sand, gravel or a mixture thereof and optionally can comprise a covering of vegetation. The substrate serves as a carrier material for the biofilm of the microorganisms.
The surface of planted and unplanted filters, through which the wastewater must penetrate for purification purposes, is dependent upon the desired wastewater volume, which is to be purified, per unit of time. Compared to so-called technical plants (e.g. SBR-methods, fixed bed systems, membrane systems) planted and unplanted soil filter systems take up a relatively large amount of surface area. In order to solve this problem, subterranean, substantially shaft-like wastewater treatment plants are known, in which the purification of wastewater is performed with an increased amount of device-related outlay. Specific approaches for the creation of local wastewater treatment plants are known e.g. from DD 300 015 A7, in which a reed bed is proposed which achieves improved ventilation through different filter-modules. The wastewater to be purified flows consecutively through these filter-modules. EP 0 738 687 A1 likewise discloses a sewage treatment plant which comprises individual filter elements, through which water to be purified flows vertically in succession. A similar plant is taught by DE 100 10 109 A1 which discloses modular filter systems, wherein the wastewater can flow through the individual filter modules for purification.
At least document WO 2011/009954 discloses a wastewater treatment plant having a plurality of filter-modules disposed one under the other, wherein each layer is connected to an intermediate store such that wastewater can be individually fed to a filter-module.
However, the problem with these wastewater treatment plants is either that in order to purify a specific quantity of wastewater, the wastewater must initially pass through a plurality of filter-modules before it can be made available again and that makes a huge area necessary or the independent activation of a single filter-module needs a lot of moving parts which do need a precise service and are costly.